Sonorous Science: Have a Cricket Tell You the Temperature!

Introduction
Do you love to hear the pulsing chirp of crickets as you fall asleep? It is an unmistakable sound. Some people find the sound pleasing and peaceful whereas others find it loud and annoying, especially if a cricket happens to find refuge from the cold inside a home. However you feel about crickets, their chirps hold a surprising message—they can report the temperature! In this activity, you'll investigate how the chirps of these tiny creatures can be used as a kind of thermometer!

Background
How is a cricket's chirp related to temperature? Crickets, like all living things, have many chemical reactions going on inside their bodies, such as reactions that allow muscles to contract to produce chirping. Crickets, like all insects, are cold-blooded and take on the temperature of their surroundings. This affects how quickly these chemical muscle reactions can occur. Specifically, a formula called the Arrhenius equation describes the activation, or threshold, energy required to make these reactions occur. As the temperature rises, it becomes easier to reach a certain activation energy, thereby allowing chemical reactions, such as the ones that allow a cricket to chirp, to occur more rapidly. Conversely, as the temperature falls, the reaction rates slow, causing the chirping to diminish along with it.

How do crickets make their distinctive chirp? They use a process called stridulation, where special body parts are rubbed together to make a noise. Generally only male crickets do this; there's a special structure on the tops of their wings, called a scraper. When they want to make their sound, they raise their wings to a 45-degree angle and draw the scraper of one wing across wrinkles on the underside of the other wing, called a file. It's somewhat like running your finger along the teeth of a comb.

Materials
• Outdoor temperature between 55 and 100 degrees Fahrenheit (12 and 38 degrees Celsius)—during an evening is ideal
• Access to an outdoor area with crickets or purchase crickets from a pet store
• Outdoor thermometer
• Stopwatch
• Piece of scratch paper and pencil or pen

Preparation
• Set up a thermometer to measure the outdoor temperature in the area where you will observe the crickets.
• While it's between 55 and 100 degrees F outside (and keeping in mind that evenings are usually best for hearing crickets chirping) go to the area where crickets are. Make sure you hear some chirping.
• Alternatively, if you purchase crickets, set them outside in a cage in the shade that allows the outside air to easily reach them. Wait until you hear chirping.

Procedure
• Pick out the chirping sound of a single cricket.
• Count how many chirps the cricket makes in 14 seconds. How many? Write this number down.
• Do this two more times, counting how many chirps the cricket makes in two more 14-second intervals. Write these numbers down. How close were the numbers to one another?
• Average the number of chirps in the 14-second intervals.
• Add 40 to the average number of chirps in 14 seconds. This equation (which is one of the oldest and easiest to use cricket-thermometer equations) is published in the Farmers' Almanac. It should give you the approximate temperature in degrees F. According to the cricket, what is the temperature?
• Check the temperature on the outdoor thermometer. How close is the temperature based on the cricket chirps to the thermometer reading? If they are different, by how much are they different? Why do you think they might be different?
• Extra: To see how accurate it is to use a cricket to tell the temperature in general, repeat this activity with different outdoor temperatures (but stay within the 55- to 100-degree F range). How accurate is the cricket at telling the temperature when it is getting warmer or colder outside? How accurate does it seem overall?
• Extra: Based on the Farmers' Almanac, you can use a cricket to tell the temperature in degrees C by counting the number of chirps in 25 seconds, dividing this number by 3 and then adding 4. According to the cricket, what is the temperature in degrees C? How accurate is this?
• Extra: For an advanced challenge, compare which equation gives the best fit with your calculated temperature data: The linear Farmers' Almanac equations (used in this activity) or the Arrhenius equation, which contains an exponential factor. Information on the Arrhenius equation can be found in the "More to explore" section on the next page. Which equation is most accurate?
• Extra: Compare the chirps of different species of crickets or different insects altogether, such as katydids. Which critter makes the best "insect thermometer"?

Observations and results
Was the temperature based on the cricket's chirps close to the actual outdoor thermometer temperature, and maybe off by only a few degrees F?

As far back as the late 1800s there have been articles published noting that a cricket's chirp rate (or number of chirps per second that it makes) changes consistently based on the outdoor temperature. There have been many equations published describing the relationship between the number of chirps per second and the temperature. These equations all vary slightly, depending on the species of cricket. Using this activity, you may have found that the cricket was within about 5 degrees F of the temperature measured using the outdoor thermometer, and probably even closer than that. If you repeated this activity multiple times and found that, based on the cricket's chirps, it's was colder than the thermometer read, this could be because the cricket was farther away from a warm building than the thermometer was, and/or because the cricket was closer to the cold soil. The snowy tree cricket is frequently cited as the most accurate at predicting temperature. If you want to listen to examples of it chirping under hot, warm, cool and cold conditions, check out the resource on the "Snowy Tree Cricket" in the "More to explore" section below.